CPack/RPM: Fix detection of RPM support for weak dependencies

Add a missing `find_program` call to populate `RPM_EXECUTABLE`.
This was left out of two previous changes that intended to query
the `rpm` executable:

* In commit 9b53eca317 (CPack/RPM: Fix weak dep support, 2021-06-29,
  v3.21.0-rc2~4^2), without `RPM_EXECUTABLE` the query always failed,
  so we were concluding that weak dependencies are not supported even
  when they are.

* In commit 488de6294a (CPack: correctly perform querytags on old
  versions of RPM, 2025-01-09, v4.0.0-rc1~182^2~3), without
  `RPM_EXECUTABLE` the query always failed.  This change has not
  yet been in a release anyway.

Also fix the test case for the "suggests" field to verify this.

Issue: #22350
Reported-by: Balazs Kosaras <[email protected]>

Modules/Internal/CPack/CPackRPM.cmake

@@ -812,6 +812,10 @@ function(cpack_rpm_generate_package)
     message(FATAL_ERROR "RPM package requires rpmbuild executable")
   endif()
 
+  # rpm is used for fallback queries in some older versions,
+  # but is not required in general.
+  find_program(RPM_EXECUTABLE rpm)
+
   # Check version of the rpmbuild tool this would be easier to
   # track bugs with users and CPackRPM debug mode.
   # We may use RPM version in order to check for available version dependent features
@@ -1077,7 +1081,7 @@ function(cpack_rpm_generate_package)
     OUTPUT_STRIP_TRAILING_WHITESPACE)
   # In some versions of RPM, rpmbuild does not understand --querytags parameter,
   # but rpm does.
-  if(NOT RPMBUILD_QUERYTAGS_SUCCESS EQUAL 0)
+  if(NOT RPMBUILD_QUERYTAGS_SUCCESS EQUAL 0 AND RPM_EXECUTABLE)
     execute_process(
       COMMAND "${RPM_EXECUTABLE}" --querytags
       OUTPUT_VARIABLE RPMBUILD_TAG_LIST
@@ -1088,16 +1092,16 @@ function(cpack_rpm_generate_package)
   # In some versions of RPM, weak dependency tags are present in the --querytags
   # list, but unsupported by rpmbuild. A different method must be used to check
   # if they are supported.
-
-  execute_process(
-    COMMAND ${RPM_EXECUTABLE} --suggests
-    ERROR_QUIET
-    RESULT_VARIABLE RPMBUILD_SUGGESTS_RESULT)
-
-  if(NOT RPMBUILD_SUGGESTS_RESULT EQUAL 0)
-    foreach(_WEAK_DEP SUGGESTS RECOMMENDS SUPPLEMENTS ENHANCES)
-      list(REMOVE_ITEM RPMBUILD_TAG_LIST ${_WEAK_DEP})
-    endforeach()
+  if(RPM_EXECUTABLE)
+    execute_process(
+      COMMAND "${RPM_EXECUTABLE}" --suggests
+      ERROR_QUIET
+      RESULT_VARIABLE RPM_SUGGESTS_RESULT)
+    if(NOT RPM_SUGGESTS_RESULT EQUAL 0)
+      foreach(_WEAK_DEP SUGGESTS RECOMMENDS SUPPLEMENTS ENHANCES)
+        list(REMOVE_ITEM RPMBUILD_TAG_LIST ${_WEAK_DEP})
+      endforeach()
+    endif()
   endif()
 
   if(CPACK_RPM_PACKAGE_EPOCH)

Tests/RunCMake/CPack/tests/SUGGESTS/VerifyResult.cmake

@@ -4,6 +4,7 @@
 execute_process(
   COMMAND ${RPMBUILD_EXECUTABLE} --nobuild test_suggests.spec
   ERROR_QUIET
+  WORKING_DIRECTORY ${CMAKE_CURRENT_LIST_DIR}
   RESULT_VARIABLE RPMBUILD_SUGGESTS_RESULT)
 
 if(RPMBUILD_SUGGESTS_RESULT EQUAL 0)
@@ -15,15 +16,20 @@ endif()
 # that tag and that was already checked by expected files test.
 if(should_contain_suggests_tag_)
   execute_process(COMMAND ${RPM_EXECUTABLE} -q --suggests -p "${FOUND_FILE_1}"
-                  WORKING_DIRECTORY "${CPACK_TEMPORARY_DIRECTORY}"
                   RESULT_VARIABLE rpm_result_
-                  OUTPUT_VARIABLE rpm_output_
-                  ERROR_VARIABLE error_variable_
+                  OUTPUT_VARIABLE rpm_stdout_
+                  ERROR_VARIABLE  rpm_stderr_
                   OUTPUT_STRIP_TRAILING_WHITESPACE)
 
-  if(rpm_result_ OR NOT rpm_output_ STREQUAL "libsuggested")
-    message(FATAL_ERROR "RPM_SUGGESTED package error: no suggested packages"
-        " (result: '${rpm_result_}'; output: '${rpm_output_}';"
-        " error: '${error_variable_}')")
+  if(rpm_result_ OR NOT rpm_stdout_ STREQUAL "libsuggested")
+    string(REPLACE "\n" "\n  " rpm_stdout_ "${rpm_stdout_}")
+    string(REPLACE "\n" "\n  " rpm_stderr_  "${rpm_stderr_}")
+    message(FATAL_ERROR "RPM_SUGGESTED package error: no suggested packages\n"
+      "result: ${rpm_result_}\n"
+      "stdout:\n"
+      "  ${rpm_stdout_}\n"
+      "stderr:\n"
+      "  ${rpm_stderr_}\n"
+      )
   endif()
 endif()